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MYCOBACTERIUM MARINUM

This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Note for Pet Owners:
Mycobacterium marinum can be transmitted from fish and marine animals directly or indirectly through water or contaminated equipment such as aquarium tanks and water-syphoning tubes to humans. So, this infectious agent is a Zoonosis and protective measures should be taken during handling to prevent transmission. 

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Description
Mycobacterium marinum is an organism that is commonly found in marine animals and water. 

Cause

The causative agent is an acid-fast mycobacterium similar to the organism which causes tuberculosis in humans. It causes tuberculosis in fish and can cause infection in humans and other species who come into contact with contaminated water (eg from fish tanks) or marine animals.

The organism thrioves at high temperatures (77oC) such as prevails in tropical aquaria.

Breed Occurrence

All fish (freshwater and marine) are susceptible to develop fish TB - especially the Anabantids, Characins and Cyprinids 

In humans the disease occurs worldwide and it  is seen in individuals exposed through work or leisure activities to contaminated water or marine animals. The incidence in the US is low, and reported to be about 0.27 cases per 100,000 population per year. Transmission of the disease has been reported following a bite from a dolphin.

Signs

In fish Mycobacterium marinum causes systemic tuberculosis in ectothermic fish. This disease is characterised by granulomas in internal organs. Other signs include :

  • Anorexia
  • Weight loss (to emaciation)
  • Bulbous eyes (exophthalmia)
  • Skin defects
  • Spinal deformities
  • Distension of the abdomen
  • Sudden death - sometimes occurs before other signs are seen

In reptiles Mycobacterium marinum infection has been reported to occur in the extremities of a collection of ectothermic Egyptian spiny-tailed lizards, Uromastyx aegyptius. These animals had been housed in a large, dry, but unsterilized tank previously used for fish. They suffered from a progressively debilitating disease and symptomatic treatment was unrewarding  Histopathology of biopsy specimens was necessary to diagnose this condition.

In humans the disease rarely affects children :

  • Usually causes localised infections following access through traumatised skin. 
  • There are 2 main types of skin lesion, which most often affect the hands :
    • Single granuloma - appears as an erythematous (pink-purple) nodule up to 3cm in diameter.
    • Ascending lymphangitic granuloma - resulting in multiple nodules,  lymphadenopathy
  • Less commonly : septic arthritis/osteomyelitis with swelling of the joint
  • Disseminated disease - rare, but seen occasionally in immune-compromised patients, and results in death

Complications
 Disseminated disease in immune-compromised patients

Diagnosis

  • Mycobacteria may be cultured from the lesions (must be conducted at 32oC). Takes 4-6 weeks
  • Identification of acid-fast mycobacteria can be made on histopathological examination of biopsies taken from the nodules :
    • Lesions less than 3 months old - acid fast bacilli in inflammatory tissue
    • Lesions 6 months old - acid fast bacilli in tuberculous granuloma
  • PCR studies (polymerase chain reaction) to identify organism

Treatment

In fish - affected individuals should be destroyed and removed form the tank. The infection will be transmitted if cannibalism occurs. NB the human health risk if handling fish or cleansing tanks.

In humans :

  • Antibiotics -need to be given for at least 2 months duration. The following have been reported successful in the treatment of human infection : 
    • Rifampin - adult humans - 600mg orally -  four doses/day. Can be given and is effective by itself.
    • Minocycline - adult humans - 100mg orally twice daily. Can be given, and is effective by itself, however resistant strains of M.marinum have been reported to occur.
    • Trimethoprim sulfamethoxazole combination - 160mg Trimethoprim/800 mg sulfamethoxazole orally every 12 hours for 10-14 days
    • Ethambutol (needs to be given in combination with another antibiotic eg rifampin) - 25mg/kg orally - four doses/day
    • Biaxin

Prognosis

The prognosis is poor for infected fish, but good for most human patients

 

Updated October 2013

 

 
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